Your goal is to grow your yeast to a cell count acceptable for your batch size and gravity. You determine this cell count using a pitching rate calculator like the one linked above. This will also help you determine the appropriate volume starter you will need in order to achieve this cell count.
As for the actual pitching process, you'll ferment about 24 hours, then put it in the fridge (still covered with sanitized foil) in order to flocculate the yeast. You'll leave it in there until the wort is clear and you have a nice layer of sediment (usually overnight, but this depends on the flocculation rate of the yeast strain). Alternatively, you can stir everything up into suspension, then transfer to sanitized, boiled, or pressure cooked mason jars and then stick those in the fridge to flocc.
Once everything is flocced, pour off the wort carefully, avoiding letting any of the sediment or visible yeast near the bottom pour out. Stop with a little wort left, then you can reapply sanitized foil, mason jar lid, or stir it all up and pour into mason jars until ready to pitch. If you do this part on brew day, then leave the yeast out a couple of hours to warm up to pitching temp. When ready to pitch, swish it around like before to get everything evenly suspended, then pitch that bitch.